I'm looking for a 3 pin oscillator
Do you mean you are looking for a 3 terminal ceramic RESONATOR, with I assume rated at 16MHz?
Oscillator is a word for a more complete circuit which includes a ceramic resonator or crystal resonator and an amplifier with feedback circuitry. The 328p internals provides the amplifier part.
Most any 3 terminal ceramic resonator will include the padding capacitors internal to the package. The two terminal varity will not. The center terminal wires to ground and the outer two terminals wire to the 328 clock pins, either end terminals to either pins.
This one will work fine: http://www.sparkfun.com/products/9420